U.S. patent number 4,985,888 [Application Number 07/451,118] was granted by the patent office on 1991-01-15 for token ring system hierarchy.
This patent grant is currently assigned to Madge Networks Limited. Invention is credited to Robert Madge, David Woodfield.
United States Patent |
4,985,888 |
Madge , et al. |
January 15, 1991 |
Token ring system hierarchy
Abstract
A communications network comprising a hierarchy of
communications systems all operating within the constraints of
token ring protocols and operationally defining a single shared
token ring. At least one of said systems is formed by a token ring
hub as disclosed and claimed in our copending application 177,764
and is connected into a system comprising the next higher
hierarchal level which may be another such token ring hub or a
token ring LAN system. Each said hub has means for receiving a
signal which indicates that the standard token ring protocols are
satisfied with respect to the direct connection of the hub of a
computer having a token ring adapter card fitted, or indicative of
such a computer connected to another said hub at a lower level of
the hierarchy. Said means transmits a comparable signal to the next
system into which the respective hub is connected in hierarchal
succession likewise indicative that the token ring protocols are
satisfied with respect to the connection of the respective hub into
the said next system.
Inventors: |
Madge; Robert (Giles,
GB2), Woodfield; David (Walsall, GB2) |
Assignee: |
Madge Networks Limited
(GB3)
|
Family
ID: |
27263402 |
Appl.
No.: |
07/451,118 |
Filed: |
December 14, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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177764 |
Apr 5, 1988 |
4905230 |
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Current U.S.
Class: |
370/405;
370/452 |
Current CPC
Class: |
H04L
12/42 (20130101) |
Current International
Class: |
H04L
12/42 (20060101); H04J 003/00 () |
Field of
Search: |
;370/85.5,17,85.12,85.13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Orsino; Joseph A.
Assistant Examiner: Sutcliffe; Geoff
Attorney, Agent or Firm: Wood, Herron & Evans
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a Continuation-in-Part of U.S. Ser. No.
177,764 now U.S. Pat. No. 4,905,230 by the same inventors, filed on
Apr. 5, 1988, and is assigned to the same assignees.
Claims
We claim:
1. A communications network comprising a plurality of computer
communications systems, all operating within the constraints of
token ring protocols, said systems being arranged in a hierarchy
which operationally defines a single, shared, token ring, said
network further comprising
(a) at least one token ring hub;
(b) a token ring LAN system into which said hub is connected to
form a subsidiary hierarchal level, each said token ring hub
further comprises means adapted to receive a signal indicative that
the requirements of the standard token ring protocols are satisfied
with respect to a computer having a token ring adapter card
connected to the hub and, in response to said signal, said means
transmits a comparable signal to said token ring LAN system into
which the hub is inserted in hierarchal succession, the transmitted
signal being likewise indicative that the requirements of the
intrinsic token ring protocols are satisfied with respect to the
connection of the hub per se into said token ring LAN system.
2. A communications network according to claim 1 in which at least
two adjacent hierarchal levels are formed by token ring hubs, one
connected into the other.
3. A communications network comprising a plurality of computer
communications systems, all operating within the constraints of
token ring protocols, said systems being arranged in a hierarchy
which operationally defines a single, shared, token ring, said
network having at least a first and a second token ring hub, said
first token ring hub being at a lower hierarchal level than the
second token ring hub and being connected thereinto , and in which
each said token ring hub in said structure further comprises means
adapted to receive a signal indicative that the requirements of the
standard token ring protocols are satisfied with respect to a
computer having a token ring adapter card connected to one of said
hubs and, in response to said signal, said means transmits a
comparable signal to another of said systems into which the hub is
inserted in hierarchal succession, the transmitted signal being
likewise indicative that the requirements of the intrinsic token
ring protocols are satisfied with respect to the connection of the
hub per se into said another system.
Description
TECHNICAL FIELD
This invention relates to a token ring implementation of local area
networks (LANS) for computer communications.
BACKGROUND TO THE INVENTION
It is known to couple a LAN system in which computers are arranged
to communicate with one another using one set of protocols to
another LAN system of computers using a different set of protocols.
Such set-ups necessarily employ software programs to enable signals
to be transferred between the systems without violation of the
respective protocols. The need for special software would also be
manifest when transferring communications between two computer
communications systems of the same type because each system has its
own specific environment in which computer calls are recognized and
services. It therefore follows that all such combined systems,
needing software interfacing, lack transparency between their parts
and any hierarchal structure would bring in train unmanageable
complications.
The present invention is directed towards facilitating a hierarchal
structure of computer communications systems, all operating within
the constraints of token ring protocols, wherein at least one of
the systems comprising the hierarchal structure has a core
comprising a token ring hub as described and disclosed in our
aforesaid copending application Ser. No. 177,764 and another one of
the systems may be either a token ring LAN system or comprise a
further token ring hub as aforesaid. Each such token ring hub is
characterized by having means adapted to receive a signal
indicative that the requirements of the standard token ring
protocols are satisfied with respect to a computer connected
directly or indirectly to the hub and in response to said signal to
forward a comparable signal to the next system into which the hub
is inserted in hierarchal succession. The latter signal is likewise
indicative that the requirements of the intrinsic protocols are
satisfied with respect to the connection of the hub per se into
said next system. In the present context, a hierarchal connection
is a connection which has the capability of at least one further
connection to it so as to form one link in a possible chain of
connections. Each such connection also facilitates one or more
merging connection. "Transparency" in the present context means
that the effect of a connection is to physically and electrically
enlarge a pre-established token ring and the effect of a
disconnection is to physically and electrically reduce the said
token ring, all without any interference in communications
proceeding between existing or remaining elements of the ring. When
another system is connected in this way the elements of the other
system may be communicated with as though they are pre-existing
members of the ring into which they are added.
Thus it is an object of the invention to provide a computer
communications system in which some of the parts have hierarchal
relationships with other parts. It is also an object of the
invention to provide a hierarchal system in which the parts are
adapted to a token ring topology and may be coupled to a LAN
computer communications system implemented as a token ring.
These objects and features of the invention are further described
hereinafter by way of example and with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 (prior art) shows diagrammatically a local area network
(LAN) implemented as a token ring;
FIG. 2 shows a representative trunk coupling device (or socket
outlet) for several work stations as used in the art in respect of
token ring installations;
FIGS. 3(a) and 3(b) show, in schematic functional form, a token
ring expansion hub unit;
FIG. 4 shows in more detail the circuit arrangement of the unit
illustrated schematically in FIG. 3.
FIG. 5 shows the use of token ring hubs as described herein and
claimed in our aforesaid copending U.S. application Ser. No.
177,764 to form a hierarchal computer communications network in
conjunction with an existing (prior art) LAN implemented as a token
ring.
Referring to the drawings, in FIG. 1 there is shown schematically
the standard implementation of a simple token ring LAN 1 such as
may be installed in a suite of offices. The details of the
implementation may be derived from BSI DD 136, ISO 8082, or IEEE
802.5. The ring comprises essentially a looped or endless
communication channel or bus 10. A bus outlet is provided in each
office or work area, there being eight shown in all, comprising
outlets 11-18. Corresponding with each outlet there is shown a work
station or personal computer 11a-18a. As seen , work stations 11a
and 13a-18a are all coupled into the ring and form part of it. Work
station 12a, however, is bypassed and as a consequence is isolated
from the ring. Whenever any of the work stations are electronically
withdrawn from or are physically disconnected from the token ring
LAN the associated ends of the bus are re-joined so that the ring
is always continuous. This effect is shown more clearly in FIG.
2.
It is sometimes necessary to provide a plurality of outputs for the
token ring LAN at the same location and a trunk coupling device 20,
represented in FIG. 2, is specified for this purpose. Such a device
may be thought of as a fixed three-way socket having the bus 10
connected to it on either side. Within the device are three socket
outlets, 21, 22, 23, each of which is adapted to receive a
standardized plug (not shown) by means of which a respective
computer may be coupled into the ring. The trunk coupling device
has three computers (21a-23a) connected to it, each comprising a
separate work station using the token ring LAN to communicate with
one another and/or to other work stations around the ring. Computer
21a is offline and hence, though physically connected to the trunk
coupling device, there is no electrical connection into the bus 10,
which is shown as bypassing this computer. The computer 22a has the
"token", being actively connected onto the bus 10. The latter is
therefore diverted through the computer transmitter and receiver
data input/output lines. Computer 23a is online and in a ready
state but is not transmitting at the instant shown. As in the
previous instance, the bus is diverted through the computer
input/output circuits. In actuality the circuits are normally
coupled through transformer windings and there is no direct
physical electrical connection between the computer circuits and
the LAN data lines.
FIGS. 3a and 3b show an example of the token ring hub unit 30
employed in the invention. It comprises two electrically connected
circuits 30a and 30b housed within a unitary casing and a wander
lead 31a which is connected at one end to an outlet port E of the
circuit 30b and at its other, free, end to a connector 31b shown
only by its electrical terminals, which plugs into a tank coupling
device. The circuit of FIG. 3a comprises a multi-socket expander.
The circuit of FIG. 3b comprises the expander outlet, also called
"a trunk insertion unit", interfacing the port E.
In its offline, closed down, condition the unit 30 comprises two
separate closed-loop, or endless, lines, namely a transmitter line
34 and a corresponding receiver line 35, each of which passes
successively through socket areas A-D of expander 30a and the trunk
insertion unit interfacing port E. There is also a biasing signal
direct current line 36 comprising leads 36a and 36b which may be
traced from an open circuited end at F through to the trunk
insertion unit at G. This additional line also passes successively
through each socket area A to D. Both the connector 31b, which
plugs into a trunk coupling unit, and the sockets of the expander
are standardized elements and are comparable in size with standard
domestic telephone plug and socket connectors. The unit 30 can be
of quite modest proportions, well adapted to being carried around
and for being moved from one room, or location, to another. As
shown, it has four sockets, but it may be provided with more
sockets or fewer than four. In use the token ring hub may serve as
a "stand alone" device, i.e. as a portable token ring not having
any connection to a LAN and permitting a limited number of work
stations in the same locality to communicate with each other.
Alternatively it may serve as an expander, permitting several work
stations grouped relatively closely together to be flexibly located
and all have access to a token ring LAN as well as to one another.
In principle, and subject to the limitations laid down for token
ring topology, token ring hubs according to the invention can also
be piggy-backed.
Each socket area A-D includes a respective physical socket (not
shown) for receiving a connector (also not shown) with the
necessary provisions for electrical contact and each essentially
comprises a multi-pole ganged relay actuated set of contacts
32(a-d), 33(a-d) and an associated relay (37a-d). Associated with
each socket area is an auxiliary relay circuit, including relays
38a-d, each of which is connected in parallel with respective
relays 37a-d, by means of which a direct current biasing signal may
be switched onto the line 36. Each socket area has associated
therewith a transmitter isolating transformer TX and a receiver
isolating transformer RX the secondary windings of which are
respectively connected under offline conditions in a closed loop
through the said contacts of the associated relay 37a-d.
Though not shown, it will be understood that the primary windings
of the aforesaid transformers are coupled via input/output circuits
of the respective computers to standard adapter cards located in
the respective computers. These adapter cards are responsible,
among other things, for instituting the protocol procedures at the
physical level involving the connection of the respective computers
onto a token ring. Before effective connection of a computer to
such a token ring is permitted these cards automatically carry out
a standard sequence of tests to ensure that the electrical
connections onto the ring will comply with the Standards
specifications.
The adapter cards have a precisely similar function with respect to
the connection of respective computers onto the present device. In
the course of the aforesaid tests a signal is applied by the
adapter card to the direct current signal terminals marked OV, +V,
at the respective socket. This signal is detected by the respective
switch circuit (39a-d) and at the end of a prescribed period,
determined by a respective timer in the switch circuit (39a-d) a
bias signal is applied to the respective parallelly connected
relays. This has the effect of switching the secondary windings of
the transmitter receiver transformers coupled to the input/output
circuits of the computer, into the corresponding parts of the lines
34, 35, and it also connects the bias signal which is provided by
the associated computer adapter card onto the signal line 36 for
forward signalling purposes. In the event that the token ring hub
30 is already functionally coupled to a token ring LAN as a
consequence of another computer being previously coupled to the
hub, the computer is then inserted into the token ring LAN via the
trunk insertion unit 30b. In the event that the connection to the
token ring LAN still has to be established, the biasing voltage at
G, under the control of protocol testing circuitry 40a and b in the
trunk insertion unit 30b then signals the socket relay in the trunk
coupling device 20 to make the connection onto the token ring LAN
and also trips relay 41 in the trunk insertion unit 30b so as to
connect the hub ring to the ring of the LAN. Suitable circuit
arrangements provided in the trunk insertion unit 30b carry out
appropriate tests essential in order to satisfy the protocol
requirements.
In FIG. 4a and b is shown a circuit implementation of the token
ring hub unit of FIG. 3. Though illustrated with four work station
connection points or "socket" areas A-D (in FIG. 4a) the unit may
comprise fewer or more such circuits. As these areas are all
identical, only the circuitry associated with Area A is described
in the following.
It will be seen that the two primary windings of the transmitter
and receiver transformers are each split in half, the two halves of
each winding being coupled serially together by a respective
capacitor 52, 53. The outer halves of the two primaries are joined
serially through a resistor 54. The two inner halves are connected,
one additionally through a resistor 55, to a voltage ramp circuit
56 comprising resistors 57, 58 and capacitor 59. The output of the
ramp circuit inputs a trigger circuit 60 which, together with the
ramp circuit 56, acts as a timer. A switch circuit 61, responsive
to the timer output, sends an operating signal to the relays 37, 38
when the timer times-out in the event that a voltage is present on
the +5V power line.
Referring to FIG. 4b, which shows the trunk insertion unit, a relay
switching circuit 62, 63, similar to the relay switching circuits
32, 33 of the "sockets" but rotated electrically through
180.degree., normally patches the transmitter and receiver rings so
that each ring is closed at that location witout any external
coupling. On operation of the switches, however, when the relay
coil 64 is energized each loop is opened to receive a primary
winding of a respective transmitter or receiver input/output
coupling transformer. Relay winding 64 is responsive to a switching
circuit 65 which is controlled by a protocol circuit 66. The bias
signal line 36 incorporates a fuse 67 and is permanently coupled to
outlet connectors 68, 69.
Protocol circuit 66 receives a bias signal from the line 36 upon
successful insertion of a work station into one of the sockets A-D
and operates to inject a bias signal into a relay circuit (which
corresponds to the relay circuits of the aforesaid sockets) in the
trunk coupling device to which the trunk insertion unit is
connected.
In the inoperative state of the token ring hub the relay contacts
32(a-d), 33(a-d) complete a balanced ring network through contacts
4-6 and 3-5, and also feed a balanced a.c. signal from the
connector TX pins to the respective RX pins through contacts 13-11
and 14-12 and via the isolating transformer. With the exception of
the ring path through the switches 62, 63 of the trunk insertion
unit the components of the latter play no part in the operation of
the token ring hub when the latter is serving as a stand-alone
device.
Before a computer intended for connection onto a token ring inserts
itself into the ring its adapter card performs a series of tests.
These tests are carried out with respect to the sockets A-D of the
token ring hub. Thus the respective adapter card drives the TX pins
with an a.c. signal and checks that the a.c. signal is returned on
the RX pins. This test checks the cable between the adapter card
and the local ring hub, the transmitter and receiver transformers
of the latter, the capacitors 52, 53, and the normally closed
contacts 32, 33. If this test is successful the adapter card then
supplies a positive supply of approximately +5V, to both
transmitter pins TX, and it measures the currents drawn by the
resistors 54, 55, which return to ground via the RX pins of the
receiver transformer. If the currents drawn by the resistors are
within defined limits, implying there are no breaks, or shorts, in
any of the cable cores, the voltages are maintained on the TX pins
and the voltage at the output of the ramp circuit climbs as the
capacitor 59 charges. After 70 milliseconds the output of the
trigger circuit 60 goes low, switching on the switch circuit 61
which sends a bias signal to the relays 37, 38. This causes the
switches 32, 33 to operate, breaking the local ring connection,
breaking the a.c. loop from the TX pins to the RX pins and thus
inserting the computer into the internal ring. The adapter card
continues to monitor the currents through resistors 54, 55 all the
time that the computer is inserted and removes the voltage supply
on the TX pins if it finds any irregularity. When the voltage is
removed, either because of fault conditions or normal removal of
the computer from the ring, capacitor 59 discharges through
resistor 58 and after 70 milliseconds the relay drops out.
Capacitors 52 and 53 are used to isolate the two d.c. test current
paths and act as low impedances to signal frequencies.
When the trunk insertion unit is connected into the socket of a
trunk coupling device the token ring hub then operates as an
expander in relation to the token ring LAN to which it appears as
though it were an adapter card. The bias signal line 36 passes the
bias signal voltage level to the output connector pairs 68, 69 and
also to the test circuit 66. A voltage on connector pins 68, 69
will be present whenever one or more of the computers is connected
to the token ring hub.
When the trunk insertion unit is connected there will be resistors
present between the TX and RX pins. Direct currents will be drawn
through resistors 71, 72 in circuit 66 which turns on the
transistor 70 if it is above 1.3 milliamps. Resistors 71, 72
provide current limiting of around 100 milliamps per line. Resistor
73, in combination with resistors 74, 75 and 76, set the current
threshold for transistor 70 to turn on. When the latter turns on,
transistor 77 is switched on as a consequence of the current drawn
through resistors 78, 79 and the current through transistor 77
energises the relay 64. If the current drawn from either TX pin is
excessively high, transistor 80 will be turned on, which turns off
transistors 70, 77, and prevents the relay 64 from pulling in.
Thus relay 64 is energised if the trunk insertion unit is connected
into a socket of a trunk coupling device and the correct current is
being drawn from both of the TX pins and if one or more of the
computers are successfully inserted into the sockets of the local
ring hub. The current provided from the TX pins will energise the
relay 64 and the token ring hub will be inserted into the main
token ring of the LAN as if it were itself an adapter card.
The bias voltage level is also fed out into the trunk coupling
device to trip the socket relay of that unit. The line 36 is fused
to prevent damage to the relay contacts in the event of a direct
short.
In FIG. 5 there is shown in diagrammatical form a communications
system similar to that illustrated in FIG. 2, having a local area
network (LAN) comprising a bus 10 into which a trunk coupling
device 20 is installed. The trunk coupling device 20 comprises
three "sockets" two of which, from the left-hand side as seen in
the drawing, are filled by computers 21a and 23a. Computer 21a is
off line. Computer 23a is on line.
Connected to the right-hand socket of the trunk coupling device 20
of FIG. 5 is a hierarchal system according to the invention having
a plurality of levels in the hierarchy. This system comprises a
first token ring hub 30a as claimed in said copending application
Ser. No. 177,764, which is plugged into the trunk coupling device
20, a second token ring hub 30b also as claimed in copending
application Ser. No. 177,764, plugged into one of the expansion
sockets of the said first token ring hub 30a and an on-line
computer 22a connected into an expansion socket of the hub 30b.
Both hubs 30a, 30b are illustrated diagrammatically and show only
two respective expansion ports. Each hub may comprise two or more
such ports. For the purposes of simplification and clarity in the
Figure, only one computer (22a) is shown connected. However, it is
to be understood that any number of the available ports of these
hubs within the limits permitted by the system, may be occupied by
respective computers or by other such token ring hubs and the
expansion ports of the latter, if present, may or may not be
occupied with further computers and/or hubs. Likewise, a further
hub or hubs may be interposed between computer 22a and hub 30b.
Each of the computers has (in its respective token ring adapter
card) a bias signal generator Gs. In the case of computers 21a and
23a the signal line from the generator Gs is connected directly to
a respective receiver Rs in the trunk coupling device 20, such
being known, conventional, connections. In the case of computer 22a
as shown, the signal line from the generator Gs is connected to the
forward signalling means Fs in the token ring hub 30b to which the
computer is connected. The means Fs in hub 30b generates a biasing
signal on a line which corresponds to the signal lines between the
generators Gs of computers 21a, 23a and the respective receivers Rs
of the trunk coupling device 20. The signal line of hub 30b is
connected to a respective forward signalling means Fs of hub 30a
which in turn is connected to the receiver Rs in the respective
socket in the trunk coupling device 20. Each of the forward
signalling means Fs consists of the circuit 39, the line 36 and the
circuits 40a , 40b illustrated in FIGS. 3a and 3b, or their
corresponding implementations illustrated in FIGS. 4a, 4b. Each
circuit Fs provides a signal to the ongoing unit which is
indicative that the protocol imperatives have been satisfied with
respect to the insertion of the device containing the circuit Fs in
the token ring of the ongoing unit (or LAN). However, in this
respect it will be appreciated that all such signals are initiated
in the token ring adapter card of a computer and if no computer is
connected to either of the hubs 30, 30b, then there will be no
ongoing bias signal generated for reception by the receiver Rs of
the trunk coupling device 20.
* * * * *